Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus64 kfwd 221637 

Area forecast discussion
National Weather Service Fort Worth Texas
1137 am CDT Mon may 22 2017

main update to the forecast was to reconfigure pops/wx and sky
grids for the afternoon and evening hours based on latest

Manual surface analysis this morning revealed a stationary
baroclinic zone remained parked along the Upper Texas coast. The
isentropic upglide along the 305k Theta surface above the cooler
surface air likely explains the widespread precipitation shield
that overspread much of central and East Texas this morning. Trends
in mosaic radar imagery would suggest (and some hi-resolution
guidance confirms) that this isentropic upglide is gradually
weakening. Weakening ascent should result in a continued
reduction of the rain shield through the afternoon hours. As a
result, i've trended pops downward across eastern and southeastern
zones. In addition, much of the convection is nearly void of any
lightning and while a stray rumble of thunder or two cannot be
ruled out, a majority of the activity should be lightning-free.

Farther north across Oklahoma, a decaying complex of convection
will continue to slowly slide southeastward. Overall, the
probability of expansive re-invigoration of this convection during
the afternoon appears low, given the extensive cloudiness. Cloud
cover may thin somewhat with the late may sun and so i'll carry
just a 20 pop across northwestern zones just in case we see a slow
uptick in activity. I won't completely rule out a strong storm
this afternoon, with perhaps some near-severe hail or gusty
outflow winds.

The zonal flow aloft this morning will gradually amplify as a
shortwave trough across the Great Basin swings east and
southeastward. As this feature aloft approaches, lapse rates will
steepen upstream and an additional complex of storms (likely with
more vigor than the current one across ok) is expected to develop
and push towards the southeast. Forward propagating corfidi
vectors of around 20 to 30 knots per NAM and GFS output would
favor this potential complex racing eastward across north and
central Texas. Given current observations and latest input from hi-
res guidance, i've elected to delay the onset of this possible
convective complex into our County Warning Area. With that in mind, the highest
rain chances will be closer to the 03 UTC time frame with likely
pops across far western zones. There is some uncertainty to the
maintenance of the mesoscale convective system farther to the east, so for now will leave
inherited pops in tact. There will be a low end severe wx risk,
west of I-35 with the main hazards being strong winds and perhaps
near-severe hail.

The rest of the forecast remains unchanged and updated products
have been transmitted.



/issued 703 am CDT Mon may 22 2017/
the western metroplex taf sites have temporarily cleared this
morning, however, we expect MVFR ceilings to quickly develop this
morning as low level moisture surges northward. MVFR ceilings
should linger through the evening, but may briefly scatter in the

Showers this morning should continue near Waco, but remain
east/southeast of the Metro terminals. Additional showers will
develop this afternoon and may briefly impact the Metro sites. It
appears that the best thunderstorm chances through tonight will
remain west of all taf sites. The better storm chances will arrive
after 12z Tuesday with the arrival of a cold front.

A mainly northeast to east wind this morning will become east
southeast this afternoon as the warm front lifts to the northwest.
Wind speeds will remain less than 12 knots. We don't expect a wind
shift to the northwest, associated with the cold front, until
after 12z Tuesday.



Previous discussion... /issued 358 am CDT Mon may 22 2017/
a widespread area of showers and a couple embedded thunderstorms
prevail across much of north and central Texas early this Monday
morning. While the frontal feature responsible for the generally
east-northeasterly surface flow sits idle across the mid and
Upper Texas coast, broad and gradual ascent atop this quasi-
stationary boundary--evidenced by northward surging Theta-E values
in the 850-700 mb layer--are helping to supply the region with
some beneficial light to moderate stratiform precipitation.

Based on the recent uptick in convection to our south, it appears
another wave of ascent is presently impinging upon the
aforementioned stalled front. While a vast majority of this
additional lift looks to remain confined to The Hill Country/Upper
Texas coast, enough of an additional impetus exists to warrant
likely pops across our southeastern counties this morning where
convection should continue to steadily fill in. Given an overall
paucity of elevated instability across the northwestern half of
the cwa, elected to limit thunder chances to just "isolated" this
morning, but show likely chances roughly south and east of a
Killeen to Canton line where instability will be maximized. While
we can't rule out some small hail in any of the more robust cells
across this region, the primary hazard from storms will be locally
heavy rainfall given pwats hanging out near the climatological
maximum for this time of year, and deep warm cloud layers in
excess of 10,000 feet. As a result, some instances of mainly
nuisance flooding of low-lying areas appears possible through the
morning hours.

As this disturbance shifts east of the region later this
morning/afternoon, we may actually see a downtrend in
precipitation coverage as a brief pocket of large-scale subsidence
slides in overhead. As a result, we've trimmed pops to reflect
mainly slight chances across the northwestern 2/3rds of the
region, and low-end chance values across our far south and eastern
zones this afternoon--and even these may be somewhat overdone.
Will, however, let the dayshift assess trends later today. While
effective bulk shear values will be on the increase through this
period, it seems probable that this morning's mass of convection
near the Gulf Coast will significantly retard the return of more
appreciable instability, limiting the threat with any additional
convection to small hail.

Later this afternoon and evening, we'll turn our attention to the
north and west as several rivulets of energy embedded within the
split flow aloft migrate across Texas. The signal for an upscale-
growing mesoscale convective system towards this evening to our west was actually a bit
stronger in last night's model runs. As a result, several levels
of uncertainty plague the evening and overnight portion of this
forecast. At this time, it appears that moisture will have
returned in sufficient quantities across the western half of Texas
to support convective development from The Trans-Pecos region into
the Panhandle as a vort lobe and associated 100+ kt jet streak
overspread the area late this afternoon. Should this activity
organize and grow upscale into an MCS, forward-propagating
corfidi vectors would support an east/east-southeastward movement
towards our western/southwestern counties during the late evening
hours. As this potential complex heads east, however, it would
likely start encountering an increasingly hostile environment for
convective sustenance given (1) more limited moisture/instability
return across our western counties, (2) less impressive low-level
wind field with sub-700 mb flow less than 20 kts, and (3) the less
favorable arrival time during the late-evening hours. All of this
taken together casts considerable doubt on the severe wind/hail
potential accompanying this system. Given these uncertainties,
we'll mention the potential for some severe-caliber wind gusts and
hail entering our west/southwest counties this evening, but
latest indications are that this complex will be on a weakening
trends as it approaches our County Warning Area.

The actual surface cold front will then blast through the region
on Tuesday, bringing a renewed thrust of showers and storms to the
area. Given a pretty limited supply of buoyancy across the
northwestern half of the County Warning Area and time of day, the severe threat
here looks pretty low. A low risk for some strong to perhaps
marginally severe storms may arise across our south and eastern
counties during the late-morning and afternoon given diurnal gains
in instability. The main hazards would be marginally severe hail
and perhaps some gusty winds. Strong cold advection behind the
front will result in blustery northwest winds Tuesday across much
of the region--perhaps close to Wind Advisory criteria--and
cooler temperatures.

Any lingering precipitation should be out of the picture by
Wednesday morning, leaving US with a nice dry stretch of weather
through the rest of the week. Moisture will vigorously return
Thursday night into Friday, but Stout capping supplied by a plume
of +25 c air at 850 mb should keep convective chances at Bay
until Saturday. In the meantime, high temperatures will likely
rocket into the middle 90s out west Thursday-Saturday as a dryline
oscillates diurnally to and fro. The Saturday-Tuesday period
could start to get active again as several impulses slide in on
northwest flow aloft. While it's far too early to get into
specifics, the thermodynamic/kinematic profiles would support at
least a threat for some strong-severe thunderstorms during this
time frame.



Preliminary point temps/pops...
Dallas-ft. Worth 76 63 75 56 82 / 40 40 40 10 5
Waco 73 61 76 54 83 / 60 50 40 20 5
Paris 76 59 71 52 75 / 30 40 40 10 5
Denton 76 60 73 50 79 / 30 50 40 5 5
McKinney 75 59 74 53 79 / 30 40 40 10 5
Dallas 76 63 75 57 81 / 40 40 40 10 5
Terrell 73 61 76 54 79 / 50 40 40 10 5
Corsicana 72 63 76 55 82 / 70 50 40 20 5
Temple 73 62 76 54 83 / 60 50 40 20 5
Mineral Wells 75 59 73 50 82 / 30 50 40 10 5


Forward watches/warnings/advisories...

National Weather Service Glossary of Abbreviations